The present invention concerns a pumping unit for a machine to distribute concrete, such as for example a concrete mixer, a truck-transported pump or other suitable apparatus to distribute concrete during building operations. In particular the present invention concerns a pumping unit which is electronically controlled to optimize the pumping and delivery conditions of the concrete.
Pumping units are known which are operatively installed in machines to distribute concrete, such as for example a concrete mixer, a truck-transported pump or other, which include at least a pumping member of the double piston type, in which a hydraulic circuit alternatively commands the pistons of each cylinder to introduce the concrete into a relative distribution circuit.
In particular, in known solutions, end-of-travel detectors are associated to each cylinder, which detect the limit position of the pistons so as to influence a consequent inversion of command of the hydraulic circuit and therefore, to determine the operating alternation of the two pistons. In this way, when one of the two pumping pistons is pushing the concrete toward the delivery valve, the other is filling up with concrete. When they have reached the end of travel, the two pistons invert their movement in order to effect the inverse cycle of delivery/filling.
In this type of known solution, the end-of-travel detectors emit a signal only when the piston has already reached the end of travel and is ready to invert its movement.
Therefore, each pumping piston stops in a substantially abrupt manner in correspondence to the end-of-travel position, the command of the hydraulic circuit is inverted and the piston starts off again at an equal speed and in an opposite direction to that in which it arrived.
This known operating condition is the cause of great noisiness and considerable vibrations, with consequent great mechanical stresses of the components, increased wear and reduction of the overall lifespan.
Moreover, as the hydraulic circuit is commanded by a combustion engine, the abrupt inversions required for the operating alternation of the pistons and the torques required to actuate this operation, cause strong variations and oscillations of the revolutions of the combustion engine, and may cause damage thereto.
A further drawback of the known solutions is the fact that, since they detect only the end-of-travel position, there is no control of the actual position of the pistons, and therefore there are difficulties in the timing of the pistons and difficulties for the fluidity of delivery of the concrete.
Document U.S. Pat. No. 5,388,965 describes a pumping cylinder including a sensor to detect one or more data relating to its functioning condition.
One purpose of the present invention is to make a pumping unit for a machine to distribute concrete which allows to reduce to a minimum the noise and vibrations.
Another purpose of the present invention is to make a pumping unit which allows to limit the oscillations of the combustion engine of the relative hydraulic command circuit depending on the torque and power required.
Further purpose of the present invention is to make a pumping unit which has easier maintenance and setting-up steps compared with the teachings of the state of the art.
A further purpose is to make a pumping unit which allows an automatic timing of the pumping pistons.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.